A voltage regulator is a device designed to provide a specific constant voltage level over a range of load conditions. It is widely used in portable electronic devices, such as a cellular phone, a laptop computer, and a personal digital assistant (PDA). Due to the requirements of low power consumption and high reliability for portable electronic devices, remarkable endeavors have been involved in the design and fabrication of voltage regulators.
In the case that the load condition of the voltage regulator is switched from one to the other, the load current outputted by the voltage regulator may change suddenly. The fast change may produce transient electrical spikes or pulses at the output voltage, causing an unfavorable effect to most electronic devices of digital circuit. Therefore, it is in need to develop a new voltage regulating apparatus with enhancement functions for the transient load change. The enhancement functions can speed up the response for the load change and, concurrently, refrain the quiescent-state current from growing up, so that performance of the voltage regulators can be improved and battery duration of the portable devices can be extended, too.